Radiation sensitive means for detecting optical flaws in glass

ABSTRACT

Apparatus for detecting flaws in a continuously moving ribbon of float-formed glass, comprising optical elements constructed and arranged to direct scanning beams of light through the glass ribbon, and which, in combination with associated discriminating means, afford a system which detects discrepancies in the transmission of light in the region of a flaw contained in the glass. In addition to the optical elements, the disclosed apparatus comprises a flaw marking unit and a control unit. Information as to the exact nature and location of marked flaws in the inspected glass may be stored in a computer, in the order of severity of the flaw. The apparatus claimed is particularly adapted to detect ream and wave flaws.

United States Patent 1191 Cushing et al.

1 1 May 29, 1973 [54] RADIATION SENSITIVE MEANS FOR DETECTING OPTICALFLAWS IN GLASS [75] Inventors: Charles J. Cushing, Churchville;

Kurt C. Schwind; Richard D. Vander Neut, both of Philadelphia,

211 Appl. No.: 251,833

[52] US. Cl ..356/239, 250/219 DF [51] Int. Cl. ..-.....G0ln 21/32 [58]Field of Search ..250/219 DF; 350/6, 350/162 SF, 285; 356/120, 167, 200,209,

[56] References Cited UNITED STATES PATENTS Potter et a1 ..356/2093,081,665 3/1966 Griss et al ..356/120 Primary Examiner-William L. SikesA ttorney-Robert D. Sanborn and Harry W. Hargis III [57] ABSTRACTApparatus for detecting flaws in a continuously moving ribbon offloat-formed glass, comprising optical elements constructed and arrangedto direct scanning beams of light through the glass ribbon, and which,in combination with associated discriminating means, afford a systemwhich detects discrepancies in the transmission of light in the regionof a flaw contained in the glass. In addition to the optical elements,the disclosed apparatus comprises a flaw marking unit and a controlunit. Information as to the exact nature and location of marked flaws inthe inspected glass may be stored in a computer, in the order ofseverity of the flaw. The apparatus claimed is particularly adapted todetect ream and wave flaws.

10 Claims, 1 1 Drawing Figures PATENIEMHZSNYS 3 736,065

Mme/14:10am;

RADIATION SENSITIVE MEANS FOR DETECTING OPTICAL FLAWS IN GLASS CROSSREFERENCE TO RELATED DISCLOSURE The present application discloses andclaims improvements in apparatus for detecting flaws in transparentmaterial, which flaws are defined as Optical Flaws. Our copendingdisclosure, Ser. No. 251,832, filed May 9, 1972, and assigned to theassignee of the present invention, discloses, but does not claim, theapparatus comprising the present invention. 7

BACKGROUND OF THE INVENTION This invention relates to apparatus fordetecting flaws in transparent material, and more particularly toimproved optical means and flaw-identifying means for use in suchapparatus. While of broader applicability, the invention has particularutility-in the inspection of sheet glass manufactured by the floatprocess.

Prior art apparatus for inspecting glass and other transparent materialshas been somewhat limited in capability for accurate detection,identification, and recording of information concerning flaws, and it isa general objective of the present invention to provide improvedapparatus overcoming such limitations.

A flaw, or defect, in a sheet of glass is considered to be anyabnormality Within or on the surface of the glass sheet, whichinterferes with the normal transmission of light. Flaws fall into twogeneral categories, known as metal flaws, with which our copending caseis particularly concerned, and optical flaws. The present invention isdirected to the detection of optical flaws, which are divided intosubcategories comprising wave and ream. A wave is an undulationoccurring repetitively on the surface of a sheet of float glass, andwhich extends in a direction generally parallel to the direction of theglass flow. A ream is a narrow band within the glass which has aneffective refractive index different from the surrounding material, andwhich also extends generally parallel to the direction of glass flow.Other conditions which present optical characteristics to the scannerthat are similar to any of the above discussed types of flaws may beclassified as one or more of those flaws.

It is an objective of this invention to provide improved glassinspection apparatus capable of both identifying and distinguishingbetween wave and ream flaws.

A further-and more specific objective of the invention is in provisionof improved optical scanning means, operable in combination withimproved electrical circuitry, to achieve identification of wave andream flaws.

SUMMARY OF THE INVENTION In achievement of the foregoing as well asother objectives,the invention contemplates provision of means forcontinuously moving a ribbon of glass along its line of length, andimproved optical means associated therewith operable continuously toscan the width of the ribbon, in detection of wave and ream flaws andand marking means for identifying the flaw (i.e. wave or ream) on theglass.

The invention is particularly featured by provision of means foroptically producing a pair of scanning beams, one for ream and the otherfor wave flaws, from a single source, and thereafter further opticallydisplacing the beams as they are redirected through the inspected glassand returned to impinge on suitably disposed photodetectors. Such anarrangement enhances capability for distinguishing between ream and waveflaws.

The manner in which the foregoing and other objectives of the inventionmay best be achieved will be more fully understood from a considerationof the following description, taken in light of the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic showing, inelevation, of the general organization of glass flaw detection apparatusembodying the invention; 7

FIG. 2 is a diagrammatic showing of the ream and wave detection opticalsystem embodied in apparatus seen in FIG. 1;

FIG. 2A is a sectional showing of a light beam taken in the planeindicated by arrows 2A-2A applied to FIG. 2;

FIG. 3 is an enlarged sectional view of a wave defect in the glass, andshowing the path of a light beam passing therethrough;

FIG. 4 is a showing of the light beam as it would appear in the planeindicated by the letter S applied to FIG. 3;

FIGS. 5 and 6 are views similar to FIGS. 3 and 4, respectively, butillustrating the path of a beam of light passing through a ream defect;

FIG. 7 is a diagrammatic illustration of the output of wave channeloptics showing reinforcement of signals for wave type defects;

FIG. 8 is an illustration similar to FIG. 7, but showing the output ofthe ream channel optics showing frequency increase of signals for reamtype defects;

FIG. 9 is a diagrammatic showing of the ream and wave signal frequencyranges; and

FIG. 10 is a schematic showing of a ream and wave signal processingcircuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With more detailedreference to the drawing, and first to FIG. 1, apparatus embodying theinvention includes an Optical Scanning Unit 10, a Control Console Unit11, and a Gun Marking Unit 12. By way of example, the above apparatusmay comprise one of four modules, each capable of scanning a section ofglass 32 inches wide, so that with four such modules, a ribbon of glass128 inches wide can be inspected continuously as it is moved along apredetermined path.

Each optical scanning unit 10 includes elements disposed above and belowthe glass undergoing inspection and comprises a Ream and Wave FlawSubsystem contemplated by the present invention, and a Metal FlawSubsystem to which our above identified copending application isdirected.

Prior to a detailed consideration of the Wave and Ream Subsystem asshown in FIGS. 2 and 2A, it will be helpful if reference is first madeto FIGS. 3 and 4, di-

rected to optical aspects of wave defect identification. Light normallyincident on a sheet of glass 24, and passing therethrough will obeySnells Law. With a wave defect, there is a change in glass thicknessfeatured by a corresponding radius of curvature as is seen at 24a, FIG.3, and the paths of the individual light rays L will be altered at thetransition points of the glass thickness changes. If the altered lightrays are projected onto a screen S, the apparent cross section of thebeam will contain alternating light and dark bars L-l and L-2,respectively, as seen in FIG. 4.

Similarly, and with reference'to FIGS. 5 and 6, ream defects 24b willchange the index of refraction of the glass 24 so that the paths of thelight rays L will be altered as seen in FIG. 5. The apparent crosssection of the beam, as viewed on screen S according to the illustrationin FIG. 6, will include corresponding light and dark bars L-l, L-2,respectively, but of lesser width than the bars seen in FIG. 4.

The Ream and Wave Flaw Subsystem is operable to detect optical flawdefects of the type described above, which defects are orientedgenerally parallel to the direction of glass flow, extending fordistances as much as several feet. With more detailed reference to FIG.2, light emanating from a source 36, such as a quartziodide lamp, isdirected through a condensing lens 37, and the resultant beam of lightis passed through a light stop aperture 38 to be reflected by a mirror39. The beam reflected by mirror 39 is interrupted by doubleslitaperture 41 to form two narrow beams of light. These two narrow beamsare then reflected by prism 42 to pass through lens 43 for reflection bya single-facet rotating mirror 45 through glass 24, onto cylindricalmirror 44. Rotating mirror 45 is located at the center of curvature ofcylindrical mirror 44, the axis of such curvature being generallyparallel to the glass and extending in the direction of glass flow.

The two outgoing beams are located to one side of the optical axis withrespect to rotating mirror 45, so that the return beams as reflected bythe mirror 44 fall to the opposite side of the optical axis of lens 43(see FIG. 2A), and are directed onto slotted apertures 46 and 47, via apair of prisms 51 and 52, respectively, for impingement on respectiveream and wave flaw detectors 53 and 54.

The important difference between the ream and wave-channels are thelocations of the beams as they strike glass 24. In especial accordancewith the invention, the wave channel beam (solid line) is close to thecenter line of the optical system, so that both the outgoing and returnbeams will pass through a defect at substantially the same instant, thusreinforcing the relatively low frequency wave defect signal, as will beappreciated from a consideration of FIG. 7. The ream channel beam(broken line) is farther from the optical axis, as is seen in FIG. 2, sothat either the outgoing beam or the return beam will pass through adefect at a given instant. Thus a pair of distinct high frequencysignals are generated by each ream defect, as will be appreciated fromFIG. 8.

The frequency of a defect signal has been shown to be related to theidentity of the defect, so that the wave and ream signals will fallwithin specific frequency ranges. If scanned by identical opticalsystems there would be an overlap in the ream and wave signalfrequencies. As will be appreciated from FIG. 9, the apparatuscontemplated by the present invention advantageously affords the abilityto optically increase the frequency separation between the wave and reamsignals, so that a distinct separation in frequency ranges is obtained.With two specific but different frequency ranges obtained from thedefects, a bandpass filtering technique is used for defectdiscrimination.

FIG. 10 illustrates circuitry employed to discriminate between the waveand ream defects. Light energy is converted to electrical energy in thephotodetectors 53 and 54. Preamplifier gain stages and 96 are used toobtain good signal-to-noise ratio, and the signals then are applied,respectively, to a pair of high pass amplifiers 97 and 98, which areused to eliminate the DC. levels of the scan signals. This is followedby a pair of channel gain adjustment amplifiers 99 and 100. Bandpassamplifiers 101 to 104 are then used to pass desired frequencies. Fullwave rectifiers 105 and 106 are used to provide single polarity outputsfrom either polarity input, and buffers 107 and 108 are used forimpedance matching. The signals are then applied to comparator circuits109 and 110. Thresholding is obtained from fixed reference voltagelevels (V ref), and the outputs are then in digital form.

Logic type gating 111 is employed to monitor a specific portion of thetotal scan signal, thereby to eliminate any false indications from theringing signal at the beginning and end of scan signals.

The optical system of the present invention is essentially that of abasic SCI-ILIEREN system modified to enhance the differentiation betweenream and wave defects. In the basic system, a mask is disposed on theoptical axis, whereas according to the present invention, a pair ofmasks of the slit-type are provided as seen at 41 in FIG. 2, one used inthe detection of ream defects and the other in the detection of wavedefects. The wave defect slit is'closer to the optical axis but notdirectly on it, whereas the ream defect slit is further from the opticalaxis. In effect, there are two SCI'ILIEREN systems, one for detectingwave defects and the other for detecting ream defects.

The optical path travelled by the light is folded by cylindrical mirror44 such that each defect will be detected twice by each scanning beam oflight. Each photodetector 53, 54 will thereforegenerate two pairs ofsignals, one pair displaced from the other according to the offset ofthe corresponding slit from the optical axis of the system.

Since the wave defect beam path is close to the optical axis, the pairof signals generated in wave photodetector 54 by a wave defect, as it istraversed by the outgoing and return wave beams, will be only slightlydisplaced timewise (right-hand portions of curves, FIG. 7), whereas thepair of signals generated in the ream photodetector 53 by a ream defectwill be greatly displaced timewise (left-hand portions of curves, FIG.8).

Since wave defects are generally wider than ream defects, a wave defectwill generate a wider signal (right-hand portions of curves, FIG. 7)than a ream defeet will (left-hand portions of curves, FIG. 8). When twosuch wide wave defect signals are superimposed (i.e. outgoing andreturn, FIG. 7), their amplitudes a, will be additive, as seen at 2a.When two narrow ream pulses, as detected by the wave detector, aresuperimposed their outputs may partially cancel, as seen in theleft-hand portion of the lower curve in FIG. 7.

Two wave defect pulses, as detected by the ream detector (right-handcurves, FIG. 8), are greatly separated. Due to this separation, there isno increase in amplitude, the result being that they produce a singlesignal of greater width (also right-hand lower curve, FIG. 8). When twonarrow pulses having a great displacement are added, as generated by aream defect (left-hand portions of curves, FIG. 8), there are producedtwo ream defect signals instead ofa single signal. These phenomena havethe effect of: increasing the amplitude of the wave defect signals inthe wave channel, while partially cancelling the ream defect signals inthe wave channel; and producing a higher frequency ream defect signal inthe ream channel by doubling the high frequency pulses, withoutincreasing the amplitude of the low frequency pulses.

Automatic marking means 12 may be of a number of known types, one ofwhich is disclosed in US. Pat. No. 3,445,672, dated May 20, 1969, andassigned to the assignee of the present invention. A preferred markingsystem is disclosed in the copending application of Charles J. Cushingand Kurt C. Schwind, Ser. No. 257,845, filed May 30, 1972, and assignedto the assignee of the present invention. Briefly, the latter systemcomprises a set of primary marking guns, a set of backup marking guns, aglass scanner for monitoring marking by the primary marking guns, andmeans for activating a backup marking gun in the event a primary gun hasfailed to mark on command.

We claim:

1. In apparatus for detecting wave and ream defects, and likeimperfections, in a sheet of glass as it is moved along a predeterminedpath, optical means having an optical axis and operable continuously toscan said sheet of glass, comprising: means for optically producing apair of spaced, outgoing scanning beams from a single source, one forthe detection of ream defects and the other for th detection of wavedefects; means for optically displacing said spaced scanning beams todirect the latter to one side of the optical axis of said optical means;means for directing said displaced beams through said sheet of glass;means for reflecting said displaced beams for return through said sheetof glass and to the other side of the optical axis of said opticalmeans; means for causing each of said displaced return beams to impingeon suitably disposed photodetectors individual to the beams; andprocessing circuit means associated with said photodetectors andeffective to detect, and distinguish between, disruptions in said lightbeams as caused by such ream and wave defects.

2. Apparatus according to claim 1, and further characterized in thatsaid means for optically producing said outgoing scanning meanscomprises a source of light; stop means positioned for impingement bysaid light and including a pair of spaced, generally parallel slitapertures disposed to one side of the optical axis of said system toform a pair of spaced beams; and a scanning mirror rotatable about apivot on said optical axis and positioned to receive said pair of spacedbeams in a region thereof disposed to one side of said pivot, saidmirror upon rotation transforming said pair of spaced beams into saidspaced, outgoing scanning beams.

3. Apparatus according to claim 1, and further characterized in thatsaid means for optically producing said spaced scanning beams comprises:means for forming a collimated beam of light; light stop means disposedin said beam of light and including a pair of spaced, generally parallelslits for forming a pair of spaced beams; focusing lens means alignedwith said optical axis and interposed in the path of said spaced beamsin such position that said beams pass through said lens means to oneside of said optical axis; and scanning mirror means positioned toreceive light from said focusing lens means, and being mounted forrotation about an axis located on said optical axis; said mirror meansand said lens means being further positioned to focus said outgoingbeams on said sheet of glass; and said mirror further being positionedfor impingement by said return beams to the other side of said opticalaxis followed by reflection of said return beams through said focusinglens means onto said photodetectors.

4. Apparatus according to claim 1, and characterized in that said meansfor producing said scanning beams is effective to displace one of saidoutgoing beams further from said optical axis than the other of theoutgoing beams.

5. Apparatus according to claim 4 and further characterized in that thepath traversed by said one outgoing beam is such that it is reflectedback through said glass in a region substantially spaced from its regionof its initial passage through the glass, thereby being effective in thedetection of ream flaws, and the path traversed by the other of saidoutgoing beams is such that it is reflected through substantially thesame region of glass as it is caused to pass initially, thereby beingeffective in the detection of wave flaws.

6. Apparatus according to claim 5 and further characterized in thatscanning is effected by a planar, rotational mirror having its center ofrotation on the optical axis of the optical means.

7. Optical means having an optical axis and operable continuously toscan a sheet of glass, in the detection of ream and wave defects, andlike imperfections, in such a sheet of glass as it is moved along apredetermined path, comprising: means for producing a pair of spaced,outgoing scanning beams, one beam for the detection of ream defects andthe other beam for the detection of wave defects; means for opticallydisplacing said spaced scanning beams to one side of the optical axis ofsaid optical means; means for directing said displaced beams throughsaid sheet of glass; means for reflecting said displaced beams forreturn through said sheet of glass and to the other side of the opticalaxis of said optical means, said one scanning beam and its reflectedcounterpart being transmitted through said glass at substantially spacedregions of the latter, said other scanning beam and its reflectedcounterpart being transmitted through said glass in substantially thesame regions of the latter; and means for causing each of said displacedreturn beams to impinge on suitably disposed photodetectors individualto the reflected beams.

8. The combination as set forth in claim 7, and further includingprocessing circuit means associated with said photodetectors andeffective to detect, and distinguish between, disruptions in said lightbeams as caused by such ream and wave defects.

9. The combination as set forth in claim 7, and characterized in thatsaid means for producing said scanning beams is effective to displaceone of said outgoing scanning beams further from said optical axis thanthe other of the outgoing beams.

10. The combination as set forth in claim 7, and characterized in thatthe recited regions of impingement of said one beam and its reflectedcounterpart are spaced a distance greater than the widths of either atypical ream or wave defect.

1. In apparatus for detecting wave and ream defects, and likeimperfections, in a sheet of glass as it is moved along a predeterminedpath, optical means having an optical axis and operable continuously toscan said sheet of glass, comprising: means for optically producing apair of spaced, outgoing scanning beams from a single source, one forthe detection of ream defects and the other for the detection of wavedefects; means for optically displacing said spaced scanning beams todirect the latter to one side of the optical axis of said optical means;means for directing said displaced beams through said sheet of glass;means for reflecting said displaced beams for return through said sheetof glass and to the other side of the optical axis of said opticalmeans; means for causing each of said displaced return beams to impingeon suitably disposed photodetectors individual to the beams; andprocessing circuit means associated with said photodetectors andeffective to detect, and distinguish between, disruptions in said lightbeams as caused by such ream and wave defects.
 2. Apparatus according toclaim 1, and further characterized in that said means for opticallyproducing said outgoing scanning means comprises a source of light; stopmeans positioned for impingement by said light and including a pair ofspaced, generally parallel slit apertures disposed to one side of theoptical axis of said system to form a pair of spaced beams; and ascanning mirror rotatable about a pivot on said optical axis andpositioned to receive said pair of spaced beams in a region thereofdisposed to one side of said pivot, said mirror upon rotationtransforming said pair of spaced beams into said spaced, outgoingscanning beams.
 3. Apparatus according to claim 1, and furthercharacterized in that said means for optically producing said spacedscanning beams comprises: means for forming a collimated beam of light;light stop means disposed in said beam of light and including a pair ofspaced, generally parallel slits for forming a pair of spaced beams;focusing lens means aligned with said optical axis and interposed in thepath of said spaced beams in such position that said beams pass throughsaid lens means to one side of said optical axis; and scanning mirrormeans positioned to receive light from said focusing lens means, andbeing mounted for rotation about an axis located on said optical axis;said mirror means and said lens means being further positioned to focussaid outgoing beams on said sheet of glass; and said mirror furtherbeing positioned for impingement by said return beams to the other sideof said optical axis followed by reflection of said return beams throughsaid focusing lens means onto said photodetectors.
 4. Apparatusaccording to claim 1, and characterized in that said means for producingsaid scanning beams is effective to displace one of said outgoing beamsfurther from said optical axis than the other of the outgoing beams. 5.Apparatus according to claim 4 and further characterized in that thepath traversed by said one outgoing beam is such that it is reflectedback through said glass in a region substantially spaced from its regionof its initial passage through the glass, thereby being effective in thedetection of ream flaws, and the path traversed by the other of saidoutgoing beams is such that it is reflected through substantially thesame region of glass as it is caused to pass initially, thereby beingeffective in the detection of wave flaws.
 6. Apparatus according toclaim 5 and further characterized in that scanning is effected by aplanar, rotational mirror having its center of rotation on the opticalaxis of the optical means.
 7. Optical means having an optical axis andoperable continuously to scan a sheet of glass, in the detection of reamand wave defects, and like imperfections, in such a sheet of glass aS itis moved along a predetermined path, comprising: means for producing apair of spaced, outgoing scanning beams, one beam for the detection ofream defects and the other beam for the detection of wave defects; meansfor optically displacing said spaced scanning beams to one side of theoptical axis of said optical means; means for directing said displacedbeams through said sheet of glass; means for reflecting said displacedbeams for return through said sheet of glass and to the other side ofthe optical axis of said optical means, said one scanning beam and itsreflected counterpart being transmitted through said glass atsubstantially spaced regions of the latter, said other scanning beam andits reflected counterpart being transmitted through said glass insubstantially the same regions of the latter; and means for causing eachof said displaced return beams to impinge on suitably disposedphotodetectors individual to the reflected beams.
 8. The combination asset forth in claim 7, and further including processing circuit meansassociated with said photodetectors and effective to detect, anddistinguish between, disruptions in said light beams as caused by suchream and wave defects.
 9. The combination as set forth in claim 7, andcharacterized in that said means for producing said scanning beams iseffective to displace one of said outgoing scanning beams further fromsaid optical axis than the other of the outgoing beams.
 10. Thecombination as set forth in claim 7, and characterized in that therecited regions of impingement of said one beam and its reflectedcounterpart are spaced a distance greater than the widths of either atypical ream or wave defect.